(1) Field of the Invention
The present invention relates to the exercise of control over the delivery of electrical current to a load in response to a monitored temperature and particularly to accurately maintaining the monitored temperature within a predetermined narrow range by controlling the delivery of current to a resistance heater. More specifically, this invention is directed to an improved temperature responsive control circuit and especially a controllable circuit for coupling a source of alternating current to an electric heater. Accordingly, the general objects of the present invention are to provide novel and simplified methods and apparatus of such character.
(2) Description of the Prior Art
Temperature responsive control circuits are, of course, well known in the art. The most common type of such prior art control circuit includes a switch which, in response to sensed temperature, is caused to assume either the "open" or "closed" state. A principal disadvantage of such prior art temperature controlled switching circuits resides in the fact that the exercise of accurate control over the temperature in the region being monitored is not possible. This inability to accurately control temperature is principally a function of the fact that the switch must be closed at a first lower temperature limit and opened at a second or upper temperature limit and the range between these limits is necessarily relatively large. This mode of operation results in a constantly fluctuating temperature which, while it cannot be eliminated, can be minimized in magnitude only through resort to complex and thus expensive control circuits.